Nana_FE_2004 When you don't get the relationship choice that you want the sims to have in CAS, the only choice you really have left is to set the relationship through MCCC. Just get both sims to the same lot and click on the MCCC option on either sim then select the Relationships menu option. Choose the option to reset a relationship. While it can be done using either sim, I find it easier and more straight forward to use the active sim. I would also recommend that once you have the mother/daughter relationship reset, that you check the other household members to make sure sibling and extended relationships are correct. Sometimes that doesn't happen and you have to reset the relationship bits for those relationships.
Hope this helps.